The present invention relates generally to a power transmission system for automotive and other vehicles and more particularly to a system wherein the speed change gear unit provided with a fluid torque converter is combined with an overdrive system.
In fluid transmission systems heretofore used for automotive vehicles, a fluid transmission system in the form of a fluid coupling or torque converter has been used to perform the functions of a clutch whereby the necessity for a clutch pedal is obviated due to the slippage occurring in the fluid transmission system which smoothly varies the resistances generated by a load. Such a fluid transmission system, however, gives rise to certain disadvantages in that fuel cost is increased due to inherent slippage and fluid losses. Thus, there arises the need for improvements in such systems whereby greater efficiency may be obtained with lowered fuel consumption. Such improvements are particularly beneficial in view of recent petroleum shortages.
Automatic transmission systems are also known wherein an overdrive system is combined with the transmission system to permit reduction in the number of engine revolutions thereby reducing fuel consumption. In such known devices, an overdrive unit is mounted at the output side of the transmission system and, as a result, the overdrive gearing must necessarily be enlarged in size in order to meet resulting torque increases and reversed rotation of the output shaft during backing of the vehicle.
The present invention contemplates provision of a power transmission system in which an overdrive unit is mounted at the input side of the speed change gear unit in such a way that the engine may be directly connected with the speed change gear unit in order to bypass the fluid transmission system, the engine being at this time connected to the gear unit by means of the overdrive unit in accordance with desired drive conditions.